AMT has a long history of use and is generally accepted as being pretty safe. But you can't approach it like meph. You're looking at one dose, (somewhere between 20 and 60mg, you should start low though) lasting you upwards of 12 hours with a 2-3 hour come up and some people get stomach issues i.e. puking, I've never had any problems like that but I take it rectally, it may make a difference. Be prepared for a fairly trippy peak, although it can vary. You won't want to snort this, I don't think it works but the smell will put you off anyway!
Also watch combinations as it's supposed to be a mild MAOI. So it could be dangerous to combine it with other serotonergic drugs, for example, although people have done so. Best not to combine it with anything unless you know exactly what you're doing. That goes for all drug use though.
6-APB I have less experience of and has not been used as widely, but again a longer come up (1hr - 1.5hr) and longer duration (6-8 hrs I think), and some people have stomach trouble.